JP3110448B2 - Overtone crystal oscillator - Google Patents

Description

Description: TECHNICAL FIELD The present invention includes a crystal oscillator having a feedback loop, and a resonance amplifier whose amplitude characteristic has an overshoot in a resonance frequency range within a feedback loop of the crystal oscillator. Related to an overtone crystal oscillator.

(Background Art) Such an overtone crystal oscillator is disclosed, for example, in Journal Funkschau, Vol. 21, 1982.
As is known from pages 81-82, it generally comprises a resonant amplifier having both capacitance and inductance. The resonance frequency of this amplifier is matched with the frequency of the desired harmonic of the crystal oscillator. In this way, the overshoot of the amplitude characteristic in the resonance frequency range of the resonance amplifier is used. In order to exactly match the resonance frequency to the desired harmonic of the crystal oscillator, precise adjustment of the resonance frequency of the resonance amplifier is necessary.

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide an overtone crystal oscillator of the type mentioned in the introduction.

In order to achieve this object, the present invention comprises a crystal oscillator having a feedback loop, and a resonance amplifier whose amplitude characteristic has an overshoot in a resonance frequency range is arranged in the feedback loop of the crystal oscillator. In the overtone crystal oscillator, the resonance frequency of the resonance amplifier is set between the frequency of the overtone to be generated and the next lower-order oscillation frequency of the crystal oscillator, and the signal within the frequency range of the overtone to be generated. On the other hand, a signal in the frequency range of the next lower-order oscillation frequency is, in a feedback loop,
Particularly, in the resonance amplifier, the overtone crystal oscillator receives a phase shift such that it cannot oscillate at the next lower-order oscillation frequency, and the overtone crystal oscillator oscillates only at the overtone frequency.

Here, “the next lower-order oscillation frequency of the crystal oscillator” means that the crystal oscillator can oscillate at a frequency (harmonic) that is an integral multiple of the fundamental frequency and the overtone frequency to be generated is, for example, 3 times the fundamental frequency. When the frequency is twice as high (third harmonic), it means the frequency of the second harmonic. Further, when the crystal oscillator can oscillate at an odd multiple of the fundamental frequency (odd harmonic) and the overtone frequency to be generated is, for example, three times the fundamental frequency (third harmonic). Means the frequency of the first harmonic (fundamental wave).

Thus, in this overtone crystal oscillator, the overshoot of the amplitude characteristic in the range of the resonant frequency of the resonant amplifier is no longer used to generate the desired overtone in this frequency range, but instead the phase of the feedback loop The change, particularly the phase change of the resonant amplifier, is used to cause the overtone crystal oscillator to oscillate at the desired overtone frequency. The phase change of the signal in the feedback loop required for this purpose is generally advantageously achieved by a resonant amplifier.

Essentially for a resonant amplifier, a signal in the frequency range of the next lower order oscillation frequency for a signal in the frequency range of the overtone to be generated, in a feedback loop,
The overtone crystal oscillator has undergone a phase shift such that it cannot oscillate at the next lower order oscillation frequencies, and the oscillation conditions are no longer satisfied for these frequencies. On the other hand, for signal frequencies above the resonant frequency of the feedback loop or resonant amplifier, there is no or very little signal phase shift, so the overtone crystal oscillator can oscillate at the overtone frequency to be generated. Thus, the oscillation conditions are satisfied for this frequency.

The main advantage of this overtone crystal oscillator is that it only needs to satisfy the condition that the resonance frequency of the resonant amplifier is located between the frequency of the overtone to be generated and the next lower order oscillation frequency of the crystal oscillator. On the point. However, since this is a fairly wide frequency range, there is no longer a need to precisely adjust the resonant frequency of the resonant amplifier, even if there are significant component variations and the resonant frequency of the resonant amplifier varies significantly. Therefore, the overton crystal oscillator of the present invention can be integrated without any problem. Further, a reliable suppression of the fundamental wave oscillation of the crystal oscillator can be obtained by a phase shift of about 180 degrees below the resonance frequency of the resonance amplifier.

In another embodiment of the invention, a signal within the frequency range of the overtone to be generated passes through the resonant amplifier with a substantially zero phase shift, and a signal within the frequency range of the next lower order oscillation frequency is generated. The resonant amplifier is characterized by undergoing a phase shift of about 180 degrees. If the crystal oscillator is implemented such that the oscillation conditions are satisfied for the desired overtone without the need to use a resonant amplifier in the feedback loop, the resonant amplifier must be able to pass signals above it at its resonant frequency. Advantageously, it is formed so as not to cause a phase shift. However, below the resonance frequency, a phase shift of about 180 degrees occurs, so that the overtone crystal oscillator cannot oscillate in this frequency range.

Another embodiment of the present invention is characterized in that a capacitor and an ohmic resistor are provided as passive elements for generating resonance in the resonance amplifier. Since a simple RC network is sufficient to generate the desired 180 degree phase shift, an overtone crystal oscillator including this RC network can be easily integrated as described above.

In order to suppress the oscillation of the overtone crystal oscillation at the next higher order oscillation frequency of the crystal oscillator with respect to the desired oscillation frequency, in another embodiment of the present invention, the feedback loop of the resonance amplifier and the crystal oscillator includes an overtone oscillator. Is characterized by having an amplitude gain smaller than 1 at the next higher-order oscillation frequency with respect to this frequency.

In a specific embodiment of the overtone crystal oscillator of the present invention, which can be easily realized, an emitter-coupled crystal multivibrator having at least two transistors is arranged as a crystal oscillator, and a differential amplifier having an RC network is used as a resonance amplifier. And a first input terminal of the differential amplifier is connected to a collector of a first transistor of the crystal multivibrator, and a first output terminal is connected to a base of a second transistor. An input terminal is connected to a collector of a second transistor of the crystal multivibrator, a second output terminal is connected to a base of the first transistor, and the differential amplifier is arranged as a feedback network of the crystal multivibrator. And

Embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(Embodiment) The emitter-coupled crystal multivibrator shown in FIG. 1 has two negative-feedback transistors 1 and 2 whose collectors are connected to the positive power supply voltage + Vp through ohmic resistors 3 and 4. It is connected to the. Resistors 3 and 4 have the function of a frequency independent feedback network. The base of transistor 1 is connected to the collector of transistor 2 and, conversely, the base of transistor 2 is connected to transistor 1
Connected to the collector. A crystal 5 is arranged between the emitters of the two transistors 1 and 2. Both emitters of transistors 1 and 2 are grounded via current sources 6 and 7, respectively.

The emitter crystal quartz multivibrator shown in FIG. 1 can be formed to oscillate at a fundamental frequency of, for example, 20 MHz. However, this crystal multivibrator can also oscillate in the region of odd harmonics. At a fundamental frequency of 20 MHz, these oscillation frequencies are relative to the third harmonic.
60 MHz and 100 MHz for the fifth harmonic.

For example, if it is necessary to generate 60 MHz as the desired overtone frequency, the crystal oscillator of FIG. 1 can be combined with the resonant amplifier shown in FIG. 2 as described below.

The resonant amplifier shown in FIG. 2 is in the form of a differential amplifier having an RC network for generating resonance.

The differential amplifier of FIG. 2 has two emitter coupled transistors 11 and 12. The two transistors 11 and 12 are connected to a positive DC power supply voltage + Vp via resistors 13 and 14, respectively. The bases of transistors 11 and 12 are connected to the same power supply voltage via resistors 15 and 16, respectively. The bases of transistors 11 and 12 are coupled via a capacitor 17. The coupled emitter of transistors 11 and 12 is a current source
Grounded via 18.

Transistor 11 for supplying an output signal to first output terminal A1
Is connected via a coupling capacitor 19 to the base of the transistor 12 corresponding to the input terminal E2. Similarly, the collector of the transistor 12 that supplies the output signal to the second output terminal A2 is a transistor corresponding to the input terminal E1.
11 is connected to the base via a coupling capacitor 20.

The resonance frequency of the resonance amplifier shown in FIG. 2 is determined by the values of the capacitors 17, 19, 20 and the resistors 13, 14. Second
If the resonance amplifier shown in the figure is combined with the crystal oscillator shown in FIG. 1 and such an overtone crystal oscillator needs to oscillate at a frequency three times the fundamental wave of the crystal oscillator shown in FIG. The resonance frequency of the differential amplifier shown in FIG. 2 needs to be located between the fundamental wave and the third harmonic of the crystal oscillator shown in FIG. In the above numerical example, the resonance frequency needs to be in the range between 20 MHz and 60 MHz. In order to reliably suppress the oscillation of the crystal oscillator at the fundamental wave in this combination arrangement, the resonance amplifier shown in FIG. 2 passes signals within a frequency range equal to or higher than the resonance frequency thereof without any phase shift. A signal in a frequency range equal to or lower than the resonance frequency of the resonance amplifier has a phase characteristic of shifting the phase by about 180 degrees.

The characteristics of the resonant amplifier shown in FIG. 2 are shown in detail in FIG.

FIG. 3 shows the frequency-amplitude characteristic of this resonance amplifier by a solid line, and the frequency-phase characteristic by a broken line.

Although not shown in FIG. 2, the amplitude characteristic of the resonance amplifier shown in FIG. 3 can be determined in a manner that two terminals of the current source are connected to the input terminals E1 and E2 of the resonance amplifier. it can. In this case, the output voltage UA has two output terminals A1 and A
Occurs between two. The ratio of the current supplied to the two input terminals E1 and E2 to the output voltage generated between the terminals A1 and A2 is shown as an amplitude characteristic in FIG. In this amplitude characteristic, an overshoot is clearly observed around 38 MHz in FIG. It is the resonance frequency of the resonance amplifier shown in FIG.

Within this range of the resonance frequency, the phase characteristic ΦA of the resonance amplifier shows a clear change. The phase characteristic ΦA indicates a phase shift that occurs between the input signal and the output signal of the differential amplifier. As is apparent from FIG. 3, there is a phase shift of about 180 degrees below the resonance frequency of the resonance amplifier. The same applies to the frequency range of the fundamental wave of about 20 MHz of the crystal oscillator shown in FIG. The resonance frequency of the resonance amplifier shown in FIG. 2 is set to 38 MHz between the frequency of the fundamental wave and the frequency of the third harmonic of the crystal oscillator shown in FIG. In this example, in the range of the overtone frequency to be generated corresponding to the frequency of the third harmonic, that is, about 60 MHz, essentially no phase shift occurs in the resonance amplifier. Have. Even in the range of the next higher-order oscillation frequency (fifth harmonic) of the crystal oscillator, that is, about 100 MHz, only a small phase shift exists in the signal passing through the resonance amplifier.

According to this embodiment of the resonant amplifier shown in FIG.
In the frequency range of the overtone to be generated (the third harmonic having a frequency of about 60 MHz in this example), the condition that almost no phase shift occurs in the signal passing through the resonance amplifier is satisfied. The next lower order oscillation frequency of the crystal oscillator (about 20 in this example)
In the range of (MHz fundamental), the signal passing through the resonant amplifier is shifted by about 180 degrees, so that the oscillation of the crystal oscillator is suppressed in this frequency range. FIG. 4 shows an overtone crystal oscillator formed from the emitter-coupled crystal multivibrator of FIG. 1 and the resonance amplifier of FIG.

The overtone crystal oscillator shown in FIG. 1 has a feedback network, in particular including resistors 3 and 4, which is a frequency-independent feedback network.

FIG. 4 shows a combination of the crystal multivibrator of FIG. 1 and the resonant amplifier of FIG. 2, in which the feedback network of the crystal multivibrator of FIG. 1 is omitted. Here, the resonant amplifier of FIG. 2 is used as a feedback network. For this purpose, the first input terminal of the resonance amplifier
E1 is connected to the collector of the first transistor 1 of the crystal multivibrator, and the output terminal A1 associated with the first input E1 is connected to the base of the second transistor 2 of the crystal multivibrator. Similarly, the second input terminal of the resonance amplifier
E2 is connected to the collector of the second transistor 2 of the crystal multivibrator, and the output terminal A2 associated with the second input E2 is connected to the base of the first transistor 1 of the crystal multivibrator. The two resistors 3 and 4 and the cross connection of the base and collector between the two transistors 1 and 2 of the crystal multivibrator are omitted. In this example, the resonant amplifier is replaced by this feedback network.

The overtone crystal oscillator shown in FIG. 4 cannot oscillate in the frequency range of the fundamental wave of the crystal oscillator. The reason is that in this frequency range, the signal passing through the resonant amplifier in the feedback loop of the crystal oscillator is shifted by about 180 degrees. However, the frequency range of the third harmonic, ie, about 60
At MHz, the overtone crystal oscillator of FIG. 4 oscillates in this frequency range because the feedback signal passes through the resonant amplifier with substantially no phase shift and its signal level does not attenuate too much. Can be.

In the frequency range of the next higher order harmonic, which is about 100 MHz, the signal passing through the resonant amplifier exhibits a small phase shift, but in this frequency range the amplitude of the signal leaving the resonant amplifier is very small and this The tone crystal oscillator no longer oscillates.

Thus, the overtone crystal oscillator shown in FIG. 4 can oscillate exclusively at its third harmonic at 60 MHz.

[Brief description of the drawings]

FIG. 1 shows an emitter-coupled quartz multivibrator, FIG. 2 shows a differential amplifier having an RC network used as a resonance amplifier, and FIG. 3 shows frequency-amplitude characteristics and frequency of the resonance amplifier of FIG. FIG. 4 shows an overtone crystal oscillator obtained by combining the crystal oscillator shown in FIG. 1 and the resonance amplifier shown in FIG. 1, 2, 5, 6, 7: Crystal oscillators 11, 12, 13, 14, 17, 18, 19, 20, 21, 22: Resonant amplifier

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H03B 5/30-5/42 INSPEC (DIALOG) JICST file (JOIS)

Claims (6)

(57) [Claims] 1. An overtone crystal oscillator comprising a crystal oscillator having a feedback loop, wherein a resonance amplifier having an amplitude characteristic having an overshoot in a resonance frequency range is arranged in a feedback loop of the crystal oscillator. Is located between the frequency of the overtone to be generated and the next lower-order oscillation frequency of the crystal oscillator, and for signals within the frequency range of the overtone to be generated, the next lower-order oscillation frequency Signal within the frequency range of
In the feedback loop, especially in the resonance amplifier, the overtone crystal oscillator undergoes a phase shift such that it cannot oscillate at the next lower-order oscillation frequency, and the overtone crystal oscillator oscillates only at the overtone frequency. An overtone crystal oscillator characterized in that: 2. A signal within the frequency range of the overtone to be generated passes through the resonant amplifier with a substantially zero phase shift, and a signal within the frequency range of the next lower order oscillation frequency is approximately 180 ° at the resonant amplifier. 2. The overtone crystal oscillator according to claim 1, wherein the overtone crystal oscillator is subjected to a phase shift. 3. The method according to claim 1, wherein the overtone to be generated is a third harmonic of the crystal oscillator, and a resonance frequency of the resonance amplifier is located between a fundamental frequency of the crystal oscillator and a third harmonic. 3. The overtone crystal oscillator according to claim 1, wherein: 4. The overtone crystal oscillator according to claim 1, wherein said resonance amplifier includes only a capacitor and an ohmic resistor as passive elements for generating resonance. 5. The feedback loop of the crystal oscillator according to claim 1, wherein at a next higher-order oscillation frequency with respect to the overtone frequency,
5. The overtone crystal oscillator according to claim 1, having an amplitude gain smaller than 1. 6. An emitter-coupled crystal multivibrator comprising at least two transistors is arranged as a crystal oscillator, a differential amplifier having an RC network is arranged as a resonant amplifier, and a first input terminal of the differential amplifier. Are connected to the collector of the first transistor of the crystal multivibrator, the first output terminal is connected to the base of the second transistor, and the second input terminal of the differential amplifier is connected to the collector of the second transistor of the crystal multivibrator. And a second output terminal connected to the base of the first transistor, wherein the differential amplifier is arranged as a feedback network of the crystal multivibrator.
The overtone crystal oscillator according to any one of -5.